1. Field of the Invention
The invention relates to a process for extracting and isolating growth factors from platelets and, more particularly, to a wound healing composition of growth factors released from mammalian platelet membranes for use in wound healing and other therapeutic uses.
2. Description of the Prior Art
The wound healing process is generally considered to occur in several stages, generally known as the healing cascade. After tissue injury, platelets are among the first cells to appear in the vicinity of the wound. Activation of a platelet by an agonist, such as thrombin, or other agonists known in the art, leads to the release of granule material from within the platelet. Such granulation activation results in the release of proteins known as growth factors, primarily concentrated in the alpha granules of platelets. Released growth factors stimulate the formation of new tissue.
When applied to wounds, growth factors are known to increase the rate of collagen laydown, vascular ingrowth, fibroblast proliferation and overall healing. The release of a protein known as platelet-derived growth factor (PDGF) is a chemotactic signal for monocytes, neutrophils and fibroblasts which then move into the wound to begin the inflammatory stage of the healing process. During this time, monocytes secrete a number of factors, including PDGF and transforming growth factor-beta 1 (TGF-β1) (also found in platelets). In this manner fibroblasts are activated to begin the repair stage of the healing process. Subsequently, wound healing continues through the process of collagen remodeling within the wound.
It is known to use activated autologous platelets as a treatment in a number of medical and surgical procedures, including but not limited to oral and maxillofacial surgery, orthopedic surgery, cosmetic and reconstructive surgery, chronic tissue repair, sports medicine injuries, neurosurgery, cardiovascular surgery, podiatry, hair transplant surgery, medical research, tissue engineering, and non-surgical cellular therapy. U.S. Pat. Nos. 4,957,742 and 6,649,072 disclose wound healing compositions that include platelet enriched plasma which prior to use is activated by thrombin to release growth factors from the alpha granules of the platelets.
Extracting therapeutic levels of platelets has been a technical challenge requiring trained cardiovascular perfusionists to operate the equipment originally designed for the production of platelet rich plasma (PRP). The clinical practitioner now has access to more simplified equipment that allows him to process PRP with smaller amounts of whole blood in a shorter amount of time. Venous access, clinical expertise, and cost are still challenges that have limited the widespread use of this process throughout the world. Moreover from a commercial standpoint, wound healing compositions that include platelets must meet costly FDA guidelines applicable to blood products.
Growth factors are responsible for the wound healing process, as described above. Platelets function merely as carriers for the growth factors. Therefore, there is a need for an inexpensive and efficient process for extracting and isolating growth factors from the platelets contained in plasma for subsequent use in wound healing. The final product preferably may be free of other components that are typically found in conventional platelet enriched wound healing products, namely the platelets themselves, ghost platelets, white blood cells, red blood cells, bacteria, and other cellular debris.
It is further desirable to prepare a wound healing product that can be subjected to conventional preservations, such as lyophilization, freeze drying, and cryopreservation in a process that does not destroy the growth factors. In this manner the shelf life of the product would be prolonged.
Therefore, there is a need for a process for isolating and extracting growth factors in a non-destructive manner from platelets. The resulting composition may or may not be substantially free of other components, such as platelets, ghost platelets, white blood cells, red blood cells and bacteria, and can be used immediately fresh or lyophilized or freeze dried into a shelf-stable product for subsequent use.